1. Field
One embodiment relates to data transmission and reception techniques suitable to be applied for reliably moving recorded data of a copy-once program between two recorders.
2. Description of the Related Art
In using “UPnP AV” as a control protocol and HTTP as a data transmission protocol in an environment using IP (Internet Protocol) as a network infrastructure, DTCP-IP as a copyright protection mechanism (DRM system; Digital Rights Management system) is used. (For example, refer to JP-A-2004-104752.)
To transmit data to a UPnP device, the transmitting party reserves the resources on the UPnP device before transmitting the data and then starts to transmit encrypted data provided by encrypting the data. To decrypt the data at the receiving party, machine authentication and key exchange (AKE) between the transmitting party and the receiving party are conducted before the data is sent.
Further, to move the data protected by DTCP-IP, simultaneous existence of the data at both the move source and the move sink is inhibited and therefore the move source must send the data while erasing the portion sent to the move sink or making the portion unreadable. (For example, refer to JP-A-2003-101529.)
Therefore, to move the data protected by DTCP-IP for inhibiting simultaneous existence of the data at both the move source and the move sink, if the data cannot be recorded reliably at the receiving party, the data is erased.
The AKE start timing is not defined in DTLA. Therefore, a server accepting data transfer from a client starts AKE at what timing is implementation dependent. This means that implementation for executing AKE after determining whether or not the data is encrypted may be adopted.
In such implementation, whether or not the data is encrypted is determined based on E-EMI of a PCP (Protected Content Packet) header in an HTTP body. Thus, to execute AKE between the client and the server of the implementation, the client must transmit an HTTP body.
However, to move the data, if the encrypted data is stored in the HTTP body and is transmitted before AKE completion, the data cannot be decrypted during the AKE processing and a part of the data (already erased at the transmitting (move) source) is lost.
In order to cope with such a situation, the following method is possible: When a request to reserve resources is sent to a UPnP device at the receiving party, the receiving party receiving the request starts AKE and then the data is transmitted according to HTTP POST. In this method, however, if the data is transmitted just after the resources are reserved, AKE is not executed and thus data not decrypted occurs and a part of the data after move cannot be played back. In the method, if AKE results in failure, the transmitting party needs to delete the reserved resources of the UPnP device at the receiving party and on the other hand, fruitless resources are temporarily left at the receiving party.